It has been known for some years, from discoveries in this laboratory, that the sparganum larva of the tapeworm Spirometra mansonoides produces a powerful growth factor, which in nearly all tests resembles pituitary growth hormone in physiological activity. It does not cross react serologically with GH, and differs from the latter in that it does not mobilize fatty acids, and is stable in blood plasma. The substance can also compensate a thyroidectomized rat, and ameliorate the condition of the diabetic rat so that the animal resumes growth and an appearance of health, although still hyperglycemic. Continuing studies are designed to further explore its physiological action, to determine whether any other species of Spirometra produces the substance, to determine how the factor works, and to characterize its molecular structure and size.